Signaling apparatus



HANS-@TTC RoosENsTElN er Al. 2,194,455

SIGNALING APPARATUS Filed Nov. 27, 1936 4 Sheets-Sheet 1 W m mum@ Y OMM E Wwf N @0.2 NSM n MM A H SIGNALING APPARATUS 'Filed Nov. 27. 195s Egan? 4 Sheets-Sheet 2 Hch 19 194- HANS-OTTO RoosENsTElN Er A1. 2,194,456

SIGNALING APPARATUS Filed Nov. 27, 1936 4 Sheets-Sheet 5 Maf ) A V0 of Heee/vel i l i AAAAAAAA' vvv INVENTORS HANS 0. SWSE/N BY MA 6 GER ATTORNEY Ch l94- HANS-OTTO RoosENsTz-:IN ET A1. 2,194,456

` SIGNALING APPARATUS Filed Nov. 27, 1936 4 Sheets-Sheet 4 NvEN'roRs HANSO. .QOOSENSE/A/ MAX 6E GER ATTORNEY Patented Mar. 19, 1940 UNETED STATES PATENT OFMQE SIGNALING APPARATUS Hans-Otto Roosenstein and Max Geiger, Berlin,

Germany, assignors to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Gery many, a corporation of Germany Application November 27, 1936, Serial No. 113,027 In Germany August 27, 1935 11 Claims. (Cl. 178-7.5)

The invention has for its object to provide the resentative of an image has always the value of possibility at television reception, of adjusting contrast 1.' The transformation at will in accordance with personal taste, two of the characteristics which determine the na- T=(w/s1)/(w/sl1) ture of an image, namely the contrast and the 5 billiellcl 0f the imuge- If the IeceiVel' is adapted reveals that the contrast depends only upon the to such purpose, the image reproduced in the 1"eratio w/s and that it remains constant thereceiver termed receiver image can be given a withcharacter diiering from the picture scanned in In the following, there will be explained the l0 the transmitter and termed transmitter image. Conditions at the control of Contrast and bm- 10 The image brilleucy H' and the image con' liancy in the television receiver. In the drawtrast T shall be defined as follows: ings Figs 1 through 4 and 5 through 10 Show n graphically relationships between operating pa- H/:Z T=ws rameters of an electro-optical reproducer and the ,1:1 n w-l-S reproduced image characteristics; while 15 Figs. 5, and 5a show embodiments of my in wherein h designates the instantaneous mean vention relating to the control of both the brightvalue of the brilliancy of a picture point for ness and contrast oi pictures. l/s-th part of a picture duration, when s is the In the receiver two controllable means exist by number of picture points for a single picture, which the contrast and the brilliancy of the image 20 and n is the instanteuecus number 0f e picture are unequivocally determined on the luminescent Peint, end w and S designate the maximum and screen, namely: The amplication of the image minimum Value 0f the picture Point brilliuucy h receiver (amplitude of the alternating potential at appearing during e trelsmisscn- Hence there the control electrode of the Braun tube) and the cOiIeslDOrlds t0 a White point 0I' black peint lebiasing potential of the control electrode of the 25 Spectively cf the transmitter image in the Te- Braun tube (background illumination). `Hitherto ceiver image a point having the brilliancy the image character has been controlled by dih=hmax= w, 01 h=hmin=8- rect operation of the control knobs assigned to Accci'dirlg t0 the defmticn, the brilliancy H' is these two means. As will be seen from the folthe meen Value 0f the Picture peint 'bliilieucy h lowing, this type of control is insufficient, since 30 considered for all points of an image. In the it is not possible to attain a state of predetermOViug imege cOutellt this mean Value difels in mined picture contrast and picture brilliancy general between the various images. Since it in a. simple and direct manner. The provision of is uct the pulpcse Of e brillialcy COTltiOL t0 imfavorable control of the image lcharacter presup- Delt et the IIIOVing ccuteut t0 all images the Seme poses the possibility of adjusting independently 35 brilliancy-otherwise the diiierence between 0f each other by means of two Operating knobs, bright and dark images, such es may fOllOW each on the one hand, the contrast at constant brilother in rapid Succession on the lm bend nancy, and on the other hand, the briuiancy at scanned in the transmitter, would become constant hardness.

i0 blurred, and the transmission distorted-it is 1n Order 130 Obtainabasis for examiningthecon- 40 necessary fOr the CGutIOl 0f the biliiancy, t0 ditions, it is necessary to consider the detection consider the mean value for all brilliances H of of the intermediate frequency, and thereby to the individual images of an entire transmission Consider certain assumptions. It beA assumed:

0r at leest during a longer time required t0 (a) That the intermediate frequency is detransmit a single frame. In assuming that this tected in the Braun tube, 45

mean value corresponds to the average value of (b) That for the picture' modulation the amgrey. there exists the equation: H=1/2 wl-S S0 plitude of the high-frequency voltage applied that, as in the cese Of contrast, 2' deDitOIl fOl across an intermediate frequency transformer to this Value is Obtained Which depends upcn the the light control electrode of the Braun tube,

content 0f an individual pictuledecreases at the most to one third of the maxi- 50 According to the denition, the contrast asmum amplitude, sumes for the Various values of w and s, the (C) That for the Braun tube, the relation- Values between 0 and l F01" w=S it has the ship between the brilliancy of the luminous spot velue 0J and fcl 8:0 0I' 011:@ its Value is and voltage at the lightcontrol electrode, i. e., p equal t0 1- Hence the transmitter signalsrepthe characteristic of the light. intensity, be estab- 55 lished by a straight line originating in the zero' point,

(d) That furthermore, in the control range to be considered, the expansion of the luminous spot does not vary to an appreciable extent, and nally,

(e) That the intermediate frequency control potential at the light control electrode of the Braun tube has a pure sine shape.

The conditions at detection will be most clearly understood on hand of a set of detection characteristics. Using; the designations vof Figure l and as long as the biasing potential U is negative and as regards its absolute value smaller than the amplitude V of the applied alternating potential, there willbe obtained for the set of detection characteristics, the expression:

and as long as U is positive and its absolute value smaller than V, the expression reads:

Contrary to the usual representation of the detection characteristic the bias may be herein treated as parameter. In this case there will be obtained the set of curves shown in Figure 2. For V U the lines approach assymptotically the Vstraight line whereby the minus sign is for the expression (l) and the plus sign for the expression (2). The tangents at the beginning of all curves have zero inclination, except in case of the straight line for U=0. The horizontal portions at the beginning of the detection characteristics and which are not contained in the analytical expressions, correspond to the case in which the bias, as regards its absolute value, is higher than the amplitude of the alternating potential, so that detection does not take place at all.

In order that for each degree of control of the Braun tube, the brilliancy values w and s may be measured at a detection characteristic, there is indicated in Figure 2 the straight lines a and b through the zero point, and having the inclinations tan and 3 tana towards the ordinate For a certain control assumed to be marked in the ordinate, these straight lines will be intersected in the corresponding height by a parallel line to the o-axis. Then the projection of the intersection points upon the detection characteristic to be considered, furnishes the desired brilliancy Values between which lie all other brilliancy values of the points as designated by h and which can possibly appear in an image at the given amplification of the image receiver and given amplitude at the amplier input.

At biasing potentials differing from zero, the detection characteristics take a curved coursethey would only have a straight jline course (bent) at rectangular curve shape of the applied alternating potential-and therefore signify a distortion in the reproduction of the brilliancy modulation, especially notable at brilliancies lying near the Value h=s.

In the following, there will be characterized the control by the maximum voltage amplitude Vm) belonging to the value of White designated by w. IThis control is proportional to the ampli cation of the image receiver at a given input Voltage at the receiver.

With the wand s-values obtained from Figure 2 there can be determined for ani7 desired control, the contrast 'I' and brilliancy H as defined. In Figure 3 the brilliancy H is shown accordingly in relation to Vrw). Figure 3 is derived from Figure 2 in that there is a transformation of the variable h to H in accordance with the equation H=1/2(w|s) which represents the grey value as pointed out above. It will be noted in this respect that the curves in Figure 3 are derived by arbitrarily drawing horizontal lines as shown in Figure 2 and reading or the values of w and s along the lines of constant bias voltage T5. The abscissa likewise now has its value transformed to represent the amplitude of the white value, which value is read oi of the curves of Figure 2 corresponding to the maximum value related to the intercept of the horizontal line. From this representation there can be easily derived for the present solution a solution even more suitable, namely the lines of constant brilliancy` H, as shown in Figure 4. These lines were obtained from Figure 3 in that for each amplitude that bias is plotted at which the brilliancy is the same. That is to say, the curves of constant brightness shown in Figure 4 are derived from Figure 3 by drawing a line parallel to the abscissa and reading off the intercepts of this parallel line with the curves representative of constant bias voltage U. Since the lines parallel to the abscissa represent lines of constant brightness by plotting the intercept value of bias voltage against Vw) the curves in Figure 4 can be drawn.

The lines of constant contrast shown in Figure 4, are straight lines through the zero point, since for the same ratio the value remains constant in accordance with Equations (l) and (2) respectively. These equations, iurthermore, furnish for each straight line the appertaining contrast. There is T=l along the line U=1/3V, since there is hereby 3:0 (Figure 2), and there will be found T=0.5 on the line U=0, since there is hereby s=1/3w. Li the region /U/ V no detection taxes place, no difference exists between w and s, and hence, there is T=0.

If, at the reproduction of the brilliancy modulation in which a part of the modulation is suppressed, regions of such distortions of the transmission are excluded, i. e, when the black values coincide with the gray values then for the brilliancy-contrast control only the region between the lines U:-1/3VV and U :i 1/3V in Figure 4 need be considered. The contrast increases in this region from 0.203 to l.. The value T=0 can thus not be obtained which however is of no consequence since in practice only brilliancy values greater than 0.5 will be of importance.

For example, if it is desired to change the brightness from 2 to 5 while maintaining the contrast constant at a value given by U=1/3V, then it will be noted that since the straight line of constant contrast U=1/3V intersects the line of constant brightness 2 at the coordinates of V(w)=5 and U=l.6. To now change to the rcquired conditions it will be noted that the line oi constant brightness 5 is intersected at the coordinates of V(w)=12 and U=i. Accordingly, the amplitude of the signals must be increased the amplitudevw) can be controlled from its from 5 to 12 while the bias `must haveits value changed from 1.6 to 4. Under these conditions there will result a change in brightness of from 2 to 5 with the constant ratio, however, maintained constant. Conversely, if it is desired to change the contrast range while maintaining the brightness constant then assuming that it is desired to change the contrast rangefrom T=0 to that where U=1/3V at a constant brightness of H=5, then the value of Vw) must be changed from 5 to 12 while the bias U is changed from 6 to 4. It is believed that these two examples will readily point out the usefulness of the derived curves shown in Figure 4.

When varying the image character as hitherto by means of the ampliiication control knob V and bias control knob U, in both cases -the contrast as well as the brilliancy will be varied, and only if there is provided a simultaneous control of amplification and bias as indicated in Fig. 4, 'such as is provided by the invention, is it possible to adjust an image for a predetermined contrast and brilliancy in a simple manner. Where the relation between amplification and bias is not provided by the control system, then one cannot obtain in a simple direct fashion the required predetermined kcontrast and brilliancy. In Figure 4 it is seen that at turning of the amplification control knob, the contrast varies in an entirely different manner according to the adjusted bias. In the prior state of practice, a denite value of contrast and brilliancy can only be achieved by cut and try in operating simultaneously or alternatively both control knobs.

As compared therewith a possibility of control of the image character, by operating on the lines of constant contrast and constant brilliancy in the diagram of Figure 4, represents an appreciable advance, as already pointed out. Also the following condition merits attention.

At the setting of the image character ordinarily no definite end state desirable of achievement presents itself, and at the setting among the various states observed, a certain state thereof is chosen. This selection can be carried out more favorably by rst adjusting a brilliancy agreeable to the eye, and thereafter attempting to obtain the most favorable contrast for this brilliancy, just as if it would be a matter of incident which contrast and brilliancy states would be encountered when operating the contro means. n

The new type of control can be practically carried out with satisfactory result, when being content with moving along straight lines having the inclination of a mean tangent at the lines of constant brilliancy in Figure 4. If, as is the case in the receiver, the amplitude V01) is con'- trolled by the grid potential of an exponential tube Uw), the control arrangement shown in Figure 5 can be employed for controlling the character of the image. In this gure the two coupled controls are provided one for controlling the contrast without affecting the brightness, and the other which controls the brightness without aiecting the contrast. This assumes that the contrast is determined by the potentials supplied to the exponential tube which controls the amplification of the received signal, and the brightness controlled by the bias voltage of the cathode ray tube. This arrangement consists of four potentiometers a, b, c and d connected in the manner shown. It is hereby assumed that by varying the voltage Uw) from Oto -20 volts.

maximum value down to the zero value. For the sake of simplicity, a linear relationship between Vw) and Uu) be assumed. 'I'hen the potentiometers a, b, and c, d must also have a linear characteristic. At a different relationship between V(w) and U(v) a linear relationship between the bias U of the Braun tube and the amplitude Vw) can again be obtained through corresponding shaping of the potentiometer characteristics. The gliding contacts coupled on the one hand at the potentiometers a and b, and on the other hand at b and d, can be moved by means of the adjustment knobs. Byl means of knob l there can be controlled the brilliancy at constant contrast, and by means of knob 2, the contrast at constant brilliancy.

The operating performance of the arrangement will now be explained.

When moving the variable contact l from any initial position to its end position, the biasing potential simultaneously with the amplitude at the Braun tube are brought to zero for any position of the variable contact 2. 'I'hus according to Figure 4, a movement along lines of constant contrast takes place, and the brilliancy will be varied (see Figures 6 and 7).

When moving the variable contact 2, there takes place a variation of vU according to Figure 8 and of Vw) according to Figure 9 for various positions of the variable contact l. There results therefrom according to Figure l0, the relationship between U and Vm). Only parallel lines are obtained Whose inclination can be set through the value of the potential difference applied to the potentiometer c. These lines correspond to the lines of constant brilliancy in Figure 4.

The range that can be covered is shaded in Figure 10. It is limited by a line of constant brilliancy belonging to the highest adjustable brilliancy, and furthermore by the positive U-axis, and by a line of constant contrast whose inclination is to be so adjusted, through suitable choice of the relative position of the potentials applied to the potentiometer c with respect to the voltage Zero point, that the equation T=1 is fuliilled. Under these conditions, the contrast can be controlled from 0 to l by means of the arrangement. The region in which the contrast is less than 0.203 thus lies within the range of control, and can however not be easily avoided when operating the control arrangement, since the distortions of the control of black appearing in the image are immediately noticeable.

In place of the circuit arrangement according to Figure 5, that according to Figure 5a, may likewise be used, and in which the end tube r of the image current amplifier feeds the one of the potentiometers across a transformer t. In

this arrangement the contrast control is derived directly from the two potentiometers 23 and 21 and not by the gain control of an exponential tube, as provided in Fig. 5.

Furthermore, in accordance with a further feature of the invention, it can be accomplished by means of kinematic arrangements of correspondlng adaptation,v that at the operation of the control knob for the biasing potential of thel Braun tube for instance, the other control knob, namely that for the amplitude of the alternating potential appearing at the control grid of the tube, will at the same time be so adjusted that the contrast of the image varies at constant image brilliancy. In this latter arrangement, the

control fknob for-the bias-of the Brauntube then serves for controlling the image contrast and that for thev amplitude of the alternating potential serves for controlling the image brilliancy at invariable image contrast.

Previously, for the control arrangement, the voltage Was considered proportional to the amplification of the image receiver, and said voltage was substituted accordinglyv by the amplification. It was hereby assumed that the factor of proportionality be constant as -set forth by the repeated reference to At given input potential at the image receiver. However at the receiver this assumption is not complied with at all. The factor of proportionality rather varies with the value of the voltage amplitude at the receiver input corresponding to Vw), for instance 1li-the apparatus is'situated at different places in which the electromagnetic eld o the transmitter differs in intensity. But a variation in the proportionality factor is identical to a shortening of the diagram in Figure i0 in the Vm) direction, i. e., the gauging ci the contrast control becomes invalid and the brilliancy varies at variation of the contrast. For the practical application of the results obtained, it is thus vnecessary that in the receiver additional amplication be provided, by Whose use it will be possible to bring the voltage Vom up to the same value at any receiver input potential existing up to a certain minimum value. Hence a kind `oi fading control is required.

Since, at a 7 m. wave, ordinarily disturbing brief fadings do not exist to an appreciable degree, it Will be sufcient to provide a third (additional) control knob at the receiver, by which the additional amplification is once readjusted Whenever the receiver operates under new conditions. In this case, the knob for the contrast ir" set to T=1 and the knob for the amplification reserve is so turned that the contrast of the image actually assumes thevvalue 1. The criterion for this is that the black value in the image assumes the color of the non-irradiated luminescent screen.

A further possibility of so varying the aforementioned proportionality factor that the control operates properly, resides in rendering adjustable at the potentiometer c, the value of the applied voltage by means of an adjustment knob. The action of this means will be readily understood on hand of Figures 6-10. In this case, the provision of an ampliiication reserve becomes superfluous. The attainable image brilliancy then varies of course directly With theinput potential at the receiver.

Moreover, it can be said that also in such cases in which the contrast and brilliancy control due to any causes can only `roughly be carried out, the advantages over the older type of control are still obtainable to the greater part.

Having described our invention, what We claim as new and desire to secure by Letters Patent is:

i. In an electro-optical device for producing an image, the method of improving the operation of the device, which comprises steps of electrooptically producing a light image from electrical signals, controlling the brightness of the image while maintaining the contrast of the image constant, and independently controlling the contrast of the image while maintaining the brightness of the image constant.

2. In a cathode ray tube wherein is provided a control electrode and a uorescent screen upon which an image is to be produced, the method -of operation whichpmprises the steps of -supplying; potentials g-to the control electrode for controlling the brightness or the image, supplying potentials to the electrode for controlling the contrast of the image, and varying both of the supplied potentials simultaneously While maintaining the brightness of the image constant While varying the contrast of the image.

3. An electro-optical device for producing an image, the method of operation which comprises the steps of simultaneously controlling the brightness of, .the image and the contrast of the image to vary the brightness of the image While maintaining the contrast of the image constant.

4. An electro-optical `device for producing an image, comprising means for electronically producinga light image, means for controlling the brightness of the image While maintaining the contrastof the image constant, and means for independently controlling the contrast of the image While maintaining the brightness of the image constant.

5. A cathode ray tube wherein is provided a control electrode and a fluorescent screen upon which an image is to be produced, comprising means for supplying potentials to the control electrode for controllingthe brightness of the image, means for supplying potentials to the electrode for controlling the contrast of the image, and means for varying both of the supplied potentials simultaneously While maintaining the brightness of the image independent of the contrast of the image.

6.\An electro-optical device for producing an image, comprising means for simultaneously controlling the brightness of the image While maintaining the contrast of the image constant, and means for varying the contrast of the image While maintaining the brightness of the image constant.

7. in a television receiver, a source of electrical signals representative of an image to be reproduced, a cathode ray tube for producing an image, means for independently controlling the brightness and contrast of the produced image Without influencing each other, and means [or supplying signals from the source to the control means. v

8. A cathode ray tube having contained therein a control electrode and a fluorescent screen for producing an image thereon, a source of electrooptical signals representative of an image to be reproduced, and means connected between the source ofsignals and the control electrode for independently controlling the brightness and contrast of the image produced on the fluorescent screen. i

9. A cathode ray tube having contained therein a control electrode and a fluorescent screen for producing an image thereon, a source of electrooptical signals representative of an image to be reproduced, and means connected between the source vof signals and thecontrol electrode for simultaneously and independently controlling the brightness and contrast of the image produced on the uorescent screen.

10. In combination,` a cathode ray tube in a television receiver, means for receiving signals representative of' an image to be reproduced, means for deriving a linearly varying voltage proportional to the image brightness to be represented by the received signals, means for simultaneously deriving an exponentially varying voltage in accordance with non-pictorial changes in picture contrast in the picture to Vbe reproduced under the control of the received signals, and means for controlling the cathode ray tube in accordance with both of the derived voltages.

11. In combination, a cathode ray tube in a television receiver, means for receiving signals representative of an image to be reproduced, means for deriving from the received signals a potential proportional to the received signals. means for simultaneously deriving a constant potential proportional to rst derived potential, and. means for supplying both of the derived potentials to the cathode ray tube.

HANS-*OTTO ROOSENSTEIN. MAX GEIGER. 

